Chemiluminescent 1,2-dioxetanes have assumed increasing importance in recent years, particularly with the advent of the enzymatically cleavable chemiluminescent 1,2-dioxetanes disclosed in Bronstein U.S. patent application Ser. No. 889,823, filed Jul. 24, 1986 (the "'823 application"); Bronstein, et al. U.S. patent application Ser. No. 140,035, filed Dec. 31, 1987; Edwards U.S. patent application Ser. No. 140,197, filed Dec. 31, 1987 (the "'197 application") and Edwards, et al. U.S. patent application Ser. No. 213,672 ("'672 application"), filed Jun. 30, 1988.
Again in marked contrast to enzymatically cleavable 1,2-dioxetanes, the various chemically cleavable chemiluminescent 1,2-dioxetanes known up to now have had little if any utility as reporter molecules in any type of analytical technique, and certainly not in bioassays. This is because the known chemically cleavable compounds are for the most part water insoluble--except for certain acetoxy-substituted 1,2-dioxetanes that are somewhat water-soluble as well as organic solvent-soluble--and thus may not be useful in biological assays unless they could somehow be modified by adding to them groups or substituents that allow conjugation to a biological species, e.g., an antibody, thus permitting such conjugated chemically cleavable 1,2-dioxetanes to be used as chemically activated chemiluminogenic labels.
The water solubility of typical enzymatically cleavable chemiluminescent 1,2-dioxetanes, on the other hand--e.g., adamantyl-appended enzymatically cleavable 1,2-dioxetanes that decompose in the presence of a suitable enzyme with light emission, such as 3-(4-methoxyspiro[1,2-dioxetane-3,2'-tricyclo[3.3.1.1.sup.3,7 ]decan]-4-phenyl phosphate and its salts, e.g., the disodium salt, identified hereinbelow in shorthand fashion as adamantylidenemethoxyphenoxyphosphorylated dioxetane ("AMPPD"), and 3-(4-methoxyspiro[1,2-dioxetane-3,2'-tricyclo[3.3.1.1.sup.3,7 ]decan]-4-yl)phenyloxy-3"-.beta.-D-galactopyranoside and its salts ("AMPGD")--makes them eminently suitable for use as reporter molecules in many types of analytical techniques carried out in aqueous media, and especially in bioassays.
It has been observed that AMPPD in aqueous solution, and also in the presence of chemiluminescence enhancers, e.g., a polymeric ammonium, phosphonium or sulfonium salt such as poly[vinylbenzyl(benzyldimethylammonium chloride)] ("BDMQ") and other heteropolar polymers (see Voyta, et al. U.S. patent application Ser. No. 203,263, filed Jun. 1, 1988), exhibits longer than optimum periods of time to reach constant light emission characteristics ("t1/2", defined as the time necessary to attain one half of the maximum chemiluminescence intensity at constant, steady-state light emission levels; this emission half-life varies as a function of the stability of the dioxetane oxyanion in various environments).
Statistically, approximately seven t1/2 periods are required to reach steady-state light emission kinetics. The t1/2 for AMPPD at concentrations above 2.times.10.sup.-5 M in aqueous solution at pH 9.5 in the presence of BDMQ has been found to be 7.5 minutes. At 4.times.10.sup.-3 M in the absence of BDMQ the t1/2 has been found to be approximately 30-60 minutes, while at 2.times.10.sup.-5 M in aqueous solution the t1/2 for AMPPD has been found to be 2.5 minutes.
In rapid bioassays that employ enzymatically cleavable chemiluminescent 1,2-dioxetanes as reporter molecules it is desirable to reach steady-state light emission kinetics as quickly as possible so as to detect an "endpoint" in the assay. And while chemiluminescence intensity can be measured before achieving steady-state kinetics, sophisticated, thermally controlled luminometry instrumentation must be used if one wishes to acquire precise data prior to steady-state emission kinetics.
Furthermore, AMPPD, in aqueous buffered solution both in the presence and the absence of chemiluminescence enhancers such as BDMQ, exhibits higher than desirable thermal and nonenzymatically activated light emission, or "noise". Such noise can be attributed to emissions from the excited states of adamantanone and of the methyl m-oxybenzoate anion derived from the aromatic portion of the AMPPD molecule. This noise can limit the levels of detection, and thus prevent the realization of ultimate sensitivity, as the measured noise level of AMPPD is approximately two orders of magnitude above the dark current in a standard luminometer.
Enzymatic cleavage of AMPPD with alkaline phosphatase also generates anionic, dephosphorylated AMPPD--adamantylidenemethoxymethylphenolate dioxetane, or AMP.crclbar.D. This phenolate anion can also be formed hydrolytically in small amounts, giving rise to a background chemiluminescence signal which, in an organized molecular assembly, such as a micelle, liposome, lamellar phase, thin layer, lipid bilayer, liposome vesicle, reversed micelle, microemulsion, microgel, latex, membrane or polymer surface, and in a hydrophobic environment such as that produced by a chemiluminescence enhancer, e.g., BDMQ, can generate strong, enhanced levels of light emission, thereby creating high background signals and substantially lowering the dynamic range of the signal resulting from enzymatic hydrolysis of AMPPD.
Consistent with the above-described observations, we have postulated the following mechanisms.
In the presence of enhancing polymers such as BDMQ: ##STR2##
Even in the absence of enhancing polymer, AMPPD can exist in aqueous solution as an aggregate: ##STR3##
In the above mechanisms, n&gt;&gt;&gt;m; n and m are a function of the presence or absence of enhancing polymer, and AMPPD concentration.
The excited state of the adamantanone singlet in aggregate form (n or m&gt;1) may exhibit higher yields of signal emission, here again particularly if "stabilized" to emit more light, as by the presence of a chemiluminescence enhancer such as BDMQ, than does the excited energy state of unaggregated adamantanone. This is perhaps due to the former's having lower singlet states, lower yields of intersystem crossing or slower intersystem crossing than the latter, or to other as yet unknown factors. Since luminometers, generally, are designed to detect all photons emitted regardless of their energy, or their wavelength, 415 nm and 477 nm chemiluminescence are both detected as background noise emissions. Similarly, when photographic or X-ray film is used to record chemiluminescence, no discrimination between the different wavelength emissions can easily be made, thus, sensitivity of detection is limited by background noise.
Finally, the observed aggregation of AMPPD under the conditions described above may result from the amphiphilic nature of AMPPD, or its phenolate anion, and like molecules: ##STR4##
It is, therefore, an object of this invention to decrease the time necessary to conduct assays, and particularly bioassays, in which enzymatically cleavable chemiluminescent 1,2-dioxetanes are used as reporter molecules.
It is also an object of this invention to provide new and improved enzymatically cleavable chemiluminescent 1,2-dioxetanes which, when used as reporter molecules in assays, and particularly bioassays, reduce the time required to complete the assay.
A further object of this invention is to provide new and improved enzymatically cleavable chemiluminescent 1,2-dioxetanes for use as substrates for enzyme-based assays, and particularly bioassays, which provide improved signal to background behavior and thus provide improved detection levels.
A still further object of this invention is to provide novel intermediates useful in synthesizing these improved enzymatically cleavable 1,2-dioxetanes.
Another object of this invention is to provide methods of preparing these enzymatically cleavable chemiluminescent 1,2-dioxetanes and intermediates therefor.
These and other objects, as well as the nature, scope and utilization of this invention, will become readily apparent to those skilled in the art from the following description and the appended claims.